Technology

SINOPEC's proprietary pygas hydrogenation technology is a two-stage catalytic hydrotreating process developed by BRICI's Yanshan Branch and engineered at commercial scale by SINOPEC Engineering Incorporated (SEI), designed to stabilize pyrolysis gasoline for gasoline blending or aromatics extraction feedstock.

Technology History and Developer

Research into pygas hydrogenation catalysts at SINOPEC began in the 1980s at the Beijing Research Institute of Chemical Industry (BRICI), Yanshan Branch, one of five SINOPEC catalyst-focused R&D institutes alongside RIPP, Fushun Research Institute, Shanghai Research Institute of Petrochemical Technology, and Shanghai Research Institute of Chemical Industry. The catalysts, YN-1 (first stage) and BY-5 (second stage), were industrialized and each won a Sinopec Science and Technology Progress Award (third prize). Process engineering and plant-level flow optimization for the "heart-cut" pygas hydrogenation configuration was carried out separately by SINOPEC Engineering Incorporation (SEI), which introduced multiple energy-saving modifications to the standard process over subsequent years.

Technology Summary and Chemistry

Pygas (C₅⁺ cut) from naphtha steam-cracking units contains diolefins, mono-olefins, aromatics, and sulfur/nitrogen/oxygen compounds that make the stream chemically unstable and prone to gum formation if left untreated. SINOPEC's technology addresses this via sequential selective hydrogenation chemistry:

• Stage 1 (diolefin removal):
  Ni-based catalyst YN-1 selectively saturates highly reactive diolefins to mono-olefins, preserving octane value while preventing polymerization/gum formation.

• Stage 2 (olefin/heteroatom removal):
  BY-5 catalyst hydrogenates remaining mono-olefins and converts sulfur, nitrogen, and oxygen compounds (sulfur to H₂S) into removable forms, producing a stabilized hydrocarbon stream.

• The chemistry is exothermic hydrogenation over supported metal catalysts (Ni for stage 1; typically CoMo/NiMo-type active phases for stage 2 desulfurization in this catalyst family), consistent with the broader industry pygas hydrotreating chemistry.

Process Flow Description

Based on the standard two-stage heart-cut pygas hydrotreating configuration that SEI engineered and optimized industrially, the process flow is as follows:

• Raw pygas is first fed to a depentanizer, splitting it into a Raw-C₅ stream and a C₆⁺ pygas stream sent forward for hydrotreating.

• The C₆⁺ pygas, combined with hydrogen, is preheated (using recycle liquid/feed-effluent exchange) and fed to the first-stage HDT reactor over YN-1, operating at mild conditions to selectively saturate diolefins while minimizing octane loss.

• First-stage reactor effluent passes to a product separator; part of the liquid is recycled to control temperature rise, excess H₂ and light ends go to the recycle gas compressor, and the separator liquid proceeds to a first-stage stabilizer column.

• The stabilized C₅⁺ liquid can be routed directly to the gasoline pool, or fractionated in a deoctanizer to isolate a C₆–C₈ heart cut for BTX extraction feed, with the C₉⁺ raffinate diverted to a hydrodealkylation unit.

• The C₆–C₈ heart cut, combined with recycle hydrogen and makeup H₂, is preheated and further heated by a charge heater before entering the second-stage HDT reactor over BY-5, where remaining olefins are saturated and sulfur is converted to H₂S.

• Second-stage effluent is cooled, separated (unreacted H₂ recycled via compressor, small purge stream vented), and the hydrotreated liquid is stabilized in a second-stage column; the bottoms product is the finished hydrotreated C₆–C₈ cut sent to aromatics extraction.

• Reported SEI process improvements include modified feed introduction, optimized heat-exchange train, reduced reflux ratio, high-efficiency heat exchangers, and cold/hot high-pressure separation in the second stage — together cutting unit energy consumption by roughly 40%.

Typical operating parameters for pygas selective hydrogenation across the industry (used here as directionally representative of SINOPEC's process, since SINOPEC-specific proprietary parameters are not publicly disclosed) are first-stage temperatures around 140°C at moderate hydrogen partial pressure and WHSV of 4–8 h⁻¹, escalating in severity through the second stage for deep desulfurization.

Technology Performance

Reported performance metrics center on selectivity and stability rather than published numerical yield tables:

• YN-1 achieves near-complete selective saturation of diolefins while preserving mono-olefins and octane value, a hallmark of the first-stage design.

• BY-5 delivers deep removal of mono-olefins, sulfur, nitrogen, and oxygen species in the second stage, producing a stabilized feed suitable for aromatics extraction or gasoline blending.

• YN-1's catalytic platform has demonstrated cross-applicability, successfully extended to cracking C₉ and C₉–C₁₀ fraction hydrogenation units beyond core pygas service, indicating robust selectivity across heavier feed matrices.

• Industry-wide reference data (non-SINOPEC-specific) show carbon balances with near-complete olefin conversion and partial aromatics retention under similar mild Pd/Ni-catalyzed conditions, offering a useful performance benchmark.

Economic Performance

Public economic data specific to SINOPEC's YN-1/BY-5 units are not disclosed in available sources; the clearest quantifiable economic signal is the approximately 40% reduction in unit energy consumption achieved through SEI's process-flow optimizations (feed mode changes, heat exchanger upgrades, reduced reflux, cold/hot high-pressure separation). This directly lowers utility costs (steam, fuel, power) per ton of pygas processed relative to earlier-generation designs, though absolute capex/opex figures were not found in the reviewed material.

Environmental Profile

The technology's environmental value proposition rests on preventing gum/polymer fouling and stabilizing a reactive petrochemical byproduct stream for safe reuse rather than disposal or flaring, aligning with SINOPEC's broader "Environmental Protection and Alternative Energy" R&D theme. The 40% energy-intensity reduction achieved through SEI's optimized heat integration and separation scheme also directly reduces the carbon and utility footprint of pygas processing units. Specific effluent/emissions data (SOx from H2S handling, hydrogen consumption efficiency, wastewater loads) for named YN-1/BY-5 installations were not found in publicly available English or Chinese sources reviewed.

Commercial Experience and Deployments

YN-1 (first-stage) and BY-5 (second-stage) catalysts have each been "successfully applied many times" in industrial pygas hydrogenation units within SINOPEC's ethylene/petrochemical complexes. 

YN-1 has additionally been deployed in cracking C₉ fraction hydrogenation units and C₉–C₁₀ fraction hydrogenation units, demonstrating deployment beyond the core pygas application.

SEI's optimized heart-cut hydrogenation process flow, including its energy-saving modifications, has been implemented at SINOPEC's petrochemical engineering projects, with documented process extensions into styrene extraction from pygas and APU (advanced process unit) configurations for increased BTX yield.

SINOPEC's broader hydroprocessing R&D ecosystem (RIPP, SCC) supports full-chain catalyst manufacturing at industrial scale, including complete technology packages for hydrogenation catalyst plants (5,000 t/y capacity).

References

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Appendix: Representative Equipment List

Based on the standard two-stage heart-cut pygas hydrotreating configuration engineered by SEI, the major equipment items typically include: